with \(u(0)=f\)  such that \(u(t)\)  is locally integrable
in \(W^1(X)\) , and \(u^{\prime }(t)\) , defined in the distributional
sense, is locally integrable in \(L^2(X)\) , and such that
the two terms on the right-hand side of
(REF ) are finite (see Section 3.12, in particular
Theorem 3.12.2, in [1]}).
